Typically, the response time of a Diesel engine (i.e., the amount of time that an engine requires to go from idle to a certain pre-selected speed) is a function of the air/fuel ratio. Decreasing the air/fuel ratio generally will decrease the response time. However, the decreased response time comes at the expense of increased exhaust smoke. Decreasing the air/fuel ratio increases the smoke produced by the engine. In many mining operations the vehicles are operated in large pits and excessive smoke may accumulate in the pits making it difficult to see. It would therefore be advantageous to make an air/fuel ratio control that optimized the air/fuel ratio for these two variables.
In addition, an optimum air/fuel ratio may change at different altitudes. At higher altitudes, the amount of oxygen present in a given volume of air is less than the amount of oxygen present in the same volume of air at a lower altitude. Thus, to maintain the proper air/fuel ratio at higher altitudes, the engine must compensate for the reduced oxygen content by increasing the volume of air mixed with the fuel or by reducing the amount of fuel in the mixture. One method for accomplishing this is to limit the rack position of the engine when it is operating at higher altitudes. One such method for limiting rack position as a function of altitude is disclosed in U.S. Pat. No. 4,368,705. However, that disclosure does not include a calculation of the optimum air/fuel ratio for response time versus smoke in terms of the vehicle altitude.
The present invention is directed toward overcoming one or more of these drawbacks.